This is an application for an RSDA KO2 award to the National Institute of Mental Health. It addresses the emotional and performance sequelae of l) acute total sleep loss, 2) chronic partial sleep loss, and 3) circadian desynchrony, in healthy adult men and women. The aim of the research is to more fully understand what happens to the mood, activation and performance of people under conditions becoming ever more prevalent in today's society. The emphasis will be on explanations that go beyond simple measures of sleepiness and failures to respond, exploring the changes in affect and information-processing ability in greater detail. The approach taken will recognize that performance decrements may occur both directly from the sleep loss and/or circadian desynchrony per se, and indirectly through the changes these stressors induce in the mood or emotional status of the individual. Apart from the obvious applied ramifications of this work regarding public wellbeing, safety and competitiveness, we consider these effects to be potential precursors to first occurrences of syndromal and sub-syndromal depression in vulnerable individuals, and to recurrence of depression in others.